There are many industrial applications for telescoping torque transmitting joints. An example is in agriculture where typically a tractor is used to tow an implement which is powered by the engine of the tractor. Torque is transmitted from the tractor to the implement by a shaft. The shaft is typically connected to both the tractor and the implement by "U" or "Cardan" joints, which permit flexing of the connection between the tractor and the implement so as to enable it to go around curves. Usually the geometry of the drive shaft with respect to the towbar connection is such that there must additionally be a telescoping connection somewhere in the drive line connecting the tractor to the implement.
The prior art has typically made such telescoping connections with a U-joint yoke attached to a sleeve with a rectangular or square internal shape which is engaged by a solid shaft attached to the yoke of the other U-joint. The shaft slides within the sleeve to provide the telescoping action necessary for operation.
Many types of telescoping elements have been used in this application but the industry is continually looking for a telescoping torque transmitting connection which will provide minimal end loading while telescoping under load, with simplicity of design, and the lowest cost possible consistent with good service life expectancy.
The assignee of the present invention has used a telescoping connection in which a square tube slides longitudinally in a square orifice formed in a billet as described above. The interacting square shapes provide torque transmission, while the difficulty of high end loading, resisting telescoping, is overcome by fitting anti-friction members or coatings on the mating members. This approach, while workable, suffers from the fact that a relatively large number of parts must be manufactured at undesirably high cost. Accordingly, this approach is not as cost-effective as might be desired.
Several attempts have been made in the prior art to simplify the design of telescoping torque transmitting shafts. Three different prior art approaches will be discussed below in connection with FIGS. 3 through 5. Basically, all those prior art approaches involve deformation of inner and outer tubes which telescope. The deformations are formed in such a way that torque can be transmitted from one of the tubes to the other. This reduces the number of parts required. However, the prior art telescoping deformed tube designs all suffer from at least one of a variety of shortcomings. Some require excessively large mating yoke members, while others, if required to be telescoped while transmitting torque, generate substantial end loading. It is therefore evident that a need exists in the art for an improved telescoping torque transmitting member.